1. Field of the Invention
The present invention relates to a copier, printer, facsimile apparatus or similar image forming apparatus operable in a duplex print mode and more particularly to an indirect image transfer type of image forming apparatus including an intermediate image transfer belt.
2. Description of the Background Art
Today, an image forming apparatus operable in a duplex copy mode for printing images on both sides of a sheet is attracting increasing attention from the resource saving standpoint. In such an apparatus, in a duplex copy mode, a color toner image formed on an intermediate image transfer belt is transferred to one side of a sheet by a secondary image transferring device and then fixed on the sheet by a fixing device. Subsequently, an image is formed on the other side of the same sheet and then fixed by the fixing device. If the apparatus is continuously operated in the duplex print mode, then consecutive sheets each carrying an image on one side thereof and heated by the fixing device contact the belt when an image is transferred to the other side. As a result, heat is transferred from the sheets to the belt and raises the temperature of the belt. Because the belt is formed of rubber or similar elastic material and therefore not resistant to heat, it stretches when heated to about 50xc2x0 C. or above.
The belt heated, in turn, heats a photoconductive drum or image carrier contacting the belt and a belt cleaner also contacting the belt. Further, the drum heated by the belt heats a developing device and a drum cleaner contacting the drum. When the developing device, drum cleaner and belt cleaner are heated to about 50xc2x0 C., toner blocking occurs.
Japanese Patent Laid-Open Publication No. 2001-92274 proposes an arrangement in which a fan cools off an intermediate image transfer belt or a belt cleaner therefor to thereby prevent toner from melting due to the heat of a fixing device. Japanese Patent Laid-Open Publication No. 2001-27833 discloses an arrangement in which a fan cools off image scanning means for the purpose of preventing the accuracy of the image scanning means from falling due to the heat of a fixing device. However, both of them are directed toward an image forming apparatus operable only in a simplex print mode.
The conventional apparatus operable in a duplex print mode additionally includes a cooling device positioned downstream of the fixing device in the direction of sheet conveyance. The cooling device cools off a sheet carrying an image on one side thereof and coming out of the fixing device. The sheet is cooled off before an image is formed on the other side thereof, thereby coping with the problem stated above. However, repeating heating and cooling is not desirable from the energy saving standpoint.
Technologies relating to the present invention are also disclosed in, e.g., Japanese Patent Laid-Open Publication Nos. 8-44220 and 2001-296755 and Japanese Patent No. 2,825,576.
It is an object of the present invention to provide an image forming apparatus operable in a duplex print mode and yet capable of reducing the influence of the heat of a fixing device and that of a sheet carrying an image fixed on one side thereof, and saving energy.
An image forming apparatus operable in a duplex print mode of the present invention includes a plurality of image carriers each for forming a particular latent image thereon. A plurality of developing devices each develop the latent image formed on the respective image carrier to thereby produce a corresponding toner images. A primary image transferring device sequentially transfers the toner images formed from the image carriers to an intermediate image transfer body one above the other to thereby complete a composite toner image. A secondary image transferring device transfers the composite toner image from the intermediate image transfer body to a recording medium. A heat pipe is held in contact with the outer periphery of the intermediate image transfer body and includes fins, which are cooled off by a fan. A press roller is held in contact with the inner periphery of the intermediate image transfer body at a position where it faces the heat pipe.
The press roller may be replaced with a plurality of press rollers in order to increase the area over which the heat pipe and intermediate image transfer body contact each other. Further, the plurality of press rollers may be replaced with a guide plate for the same purpose.